Doel 3 & Tihange 2 - Some Peer-reviewed Scientific Papers & Reports

7.3. Pressure during incidental or accidental conditions

up to 50 hours after the start of the PTS. This allows to quantify the hydrogen fugacity in the ferritic base material of the RPV during a PTS.

(a) Zoom on time dependent concentra- tion profile close to the steel-water inter- face.

(b) Zoom on the time dependent concen- tration profile at the lining-base material interface in the RPV wall.

Figure 7.12: Concentration profile of hydrogen in the RPV wall as a result of a PTS considering only corrosion generated hydrogen with a 90% absorption coefficient and a hydrogen generation rate of 150 mol H/yr. The lines show the concentration profile for different moments after the start of the PTS with an interval of 1 hour up to 50 hours. As for the radiolysis generated hydrogen, one can see that the diffusion during a PTS is much slower compared to a cold shutdown due to the fast cooling of the steel. Therefore, less hydrogen was able to escape the material and thus the concentration is higher. One can find a hydrogen fugacity equal to 4.73 10 4 Pa. This is again more than a factor of 4 lower compared to the maximum hydrogen fugacity for the same case during a cold shutdown. As noted before, this is due to the higher temperature and therefore higher Sieverts’ constant during a PTS. To be complete, the maximum hydrogen fugacities corresponding to the different cases of corrosion are calculated and shown in Table 7.4.

Table 7.4: Maximum hydrogen fugacity in the base material of the RPV due to corrosion after a PTS.

Hydrogen production rate 50 mol H/yr 150 mol H/yr f H [Pa]

Absorption efficiency

10 % 90 %

60

580

5.01 10 3

4.73 10 4

91